Conventionally, an optical analysis method has been proposed in order to perform non-destructive analysis of components contained in an object. With the optical analysis method, first the object is irradiated with light. Next, a spectral filter is used to extract light of a wavelength corresponding to a target component from transmitted light that has passed through the object or reflected light that has been reflected by the object, and the extracted light is received by a light receiving element. Absorbance is then derived, based on an output signal from the light receiving element, and the percentage of target component is furthermore calculated from the absorbance (e.g., see Patent Literatures 1 and 2).
Specifically, Patent Literature 1 discloses an analysis device that performs optical analysis with glucose contained in fruit and vegetables as the target component. With the analysis device disclosed in Patent Literature 1, since the target component is glucose, light containing wavelengths in the near-infrared region is irradiated from a light source. As for the spectral filter, a reflective spectral filter using a diffraction grating is used. This spectral filter is formed so that only light of wavelengths in a range of 700 nm to 1000 nm is guided to the light receiving element.
Patent Literature 2 also discloses an analysis device that takes glucose contained in fruit and vegetables as the target component. With the analysis device disclosed in Patent Literature 2, however, a plurality of transmissive spectral filters that transmit only light of set wavelengths are used, different from the analysis device disclosed in Patent Literature 1. The spectral filters are disposed in the same plane within the beam irradiation range. As a result of this configuration, only light from the object being measured that conforms to the set wavelength of one of the spectral filters passes through the spectral filters and is received by the light receiving element.
Incidentally, with the abovementioned optical analysis method, in the case where the target component differs, the wavelengths (selected wavelengths) of light to be extracted using a spectral filter will also differ. Consequently, with the analysis devices disclosed in Patent Literature 1 and Patent Literature 2, the spectral filter needs to be exchanged in the case of targeting components other than glucose, making it practically impossible to target components other than glucose.
On the other hand, Patent Literature 3 discloses a reflective spectral filter that enables the selected wavelength to be changed. The spectral filter disclosed in Patent Literature 3 is provided with a resonance grating, a substrate disposed such that a gap is formed therebetween, and a configuration for applying a voltage between the resonance grating and the substrate. When the magnitude of the voltage applied between the resonance grating and the substrate is changed in this spectral filter, the distance therebetween changes, resulting in reflectance relative to incident light also changing. If the spectral filter disclosed in Patent Literature 3 is used, the selected wavelength can thus be changed, and an analysis device capable of handling a wide variety of target components can conceivably be obtained.